1. Field of the Invention
This invention relates generally to X-ray tubes and is concerned, more particularly, with a multi-target X-ray tube suitable for irradiating a variety of materials.
2. Description of the Prior Art
In an X-ray spectroscopy system, the primary source of exciting X-radiation may comprise an X-ray tube of the conventional type which emits a continuous, or "white" band of X-radiation. This bremsstrahlung type of X-radiation may be employed, for example, in irradiating a sample of multi-element material to cause the irradiated elements therein to emit, simultaneously, respective characteristic lines of X-radiation which have associated energy values indicative of the emitting elements. The fluorescent X-rays, thus produced, may be detected by conventional means, such as solid state or proportional counters, for examples, which convert the incident X-rays into respective output pulses. The resulting train of output pulses from the detecting means may be separated electronically, as by a pulse height analyzer, for example, in accordance with the associated energy values of the respective pulses. In this manner, there may be produced for visual display an output energy spectrum wherein the emitting elements in the sample may be identified.
Thus, each element may be identified by its principal characteristic wavelength of fluorescent X-radiation, which is emitted most strongly when the excitation X-rays have a slightly shorter wavelength and a correspondingly higher energy level. Accordingly, when detecting a particular group of elements in a long series of samples, the spectroscopic system may conveniently be provided with X-ray source means for selectively exciting the respective elements of the group to emit most strongly their respective characteristic wavelengths of fluorescent X-radiation. This alternative X-ray source means may comprise an X-ray tube having therein an electron source suitably disposed for directing an electron beam onto a plurality of target materials. Each of the target materials, when bombarded by electrons, produces a highly intense beam of X-rays having desired wavelengths for selectively exciting one of the elements in the group of interest. As a result, the excited elements will emit strong characteristic wavelengths of fluorescent X-radiation which may be more readily detected and displayed, as described.
However, multi-target X-ray tubes generally are provided with a common electron source which is shared by the respective targets. This arrangement necessitates running the long series of samples through the field of X-radiation over and over again until each of the targets, in turn, has been bombarded by the common electron source to produce the respective associated wavelengths of X-radiation. Obviously, this repetitive process is an unnecessarily time consuming and expensive operation. Furthermore, it does not make full use of the sophisticated equipment available for detecting and separating fluorescent X-rays of varying energy values.
Therefore, it is advantageous and desirable to provide an X-ray tube having therein a plurality of target materials which may be bombarded by an electron source, simultaneously or alternatively, as desired.